One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the magnetic media to selectively read from or write to the rotating magnetic media, such as a magnetic disk.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the recording and reproducing density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult to quickly and accurately position the read/write head over the desired information tracks on the disk. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density. One conventional approach is to employ a dual-stage actuator system.
FIG. 1a-1c is a conventional disk drive unit incorporating a dual-stage actuator system. The dual-stage actuator system includes a primary actuator such as a voice-coil motor 105 and a secondary micro-actuator such as a piezoelectric micro-actuator 107. A magnetic disk 101 of the disk drive unit is mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly 106 that includes a slider 103 incorporating a read/write head, a piezoelectric micro-actuator 107 and a suspension 110 to support the slider 103 and the piezoelectric micro-actuator 107.
As the primary actuator, the voice-coil motor 105 is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider 103 to move from track to track across the surface of the disk 101, thereby enabling the read/write head to read data from or write data to the disk 101. According to the voice-coil motor 105, the piezoelectric micro-actuator 107 corrects the placement on a much small scale to compensate the vibration tolerance of the suspension 110 or the voice-coil micro-actuator 105. Thereby, the piezoelectric micro-actuator 107 enables a smaller recordable track width, and increases the tracks per inch (TPI), also, it reduces traces accessing time and positioning time. Thus, the introduction of the piezoelectric micro-actuator increases the trace density of the disk drive unit greatly.
FIG. 1b illustrates a head gimbal assembly 106 of the conventional disk drive unit with a dual-stage actuator shown in FIG. 1a. As illustrated, the suspension 110 of the head gimbal assembly 106 includes a flexure 111 with a plurality of traces, a slider support portion 112 with a bump 112a, a metal base plate 113 and a load beam 114 with a dimple 114a to support the slider support portion 112 and the metal base plate 113. The flexure 111 connects the slider support portion 112 and the metal base plate 113 by the traces thereon, the tongue region of the flexure 111 has a slider mounting region 111b for mounting the slider thereon and a piezoelectric element mounting region 111a for mounting the piezoelectric element of the piezoelectric micro-actuator 107 thereon, the slider 103 is partially mounted on the slider support portion 112 through the slider mounting region 111b. The slider support portion 112 forms a bump 112a thereon to support the center of the backside of the slider 103 and the dimple 114a of the load beam 114 sustains the bump 112a, in doing this, enabling the bump 112a to keep the load force from the load beam 114 always evenly applying to the center of the slider 103 when the slider 103 flying on the disk. The piezoelectric micro-actuator 107 includes a left thin film piezoelectric element 201 and a right thin film piezoelectric element 202 connecting with the left thin film piezoelectric element 201, the left thin film piezoelectric element 201 and the right thin film piezoelectric element 202 adhere to the piezoelectric element mounting region 111a of the flexure 111. Referring to FIG. 1c also, when a voltage is input to the two thin film piezoelectric element 201,202, one thin film piezoelectric element 201/202 thereof will contract and the other thin film piezoelectric element 202/201 thereof will expand, this will generate a rotation torque to the slider support portion 112, thus the slider support portion 112 and the slider 103 will rotate against the dimple 114a subsequently, to achieve a slider fine position adjustment.
FIG. 2 is a plan view of a conventional piezoelectric micro-actuator shown in FIG., FIG. 2a is cross-sectional view taken along line A-A of FIG. 2, and FIG. 2b is cross-sectional view taken along line B-B of FIG. 2. As is shown, a pair of electrode pads 204 are formed on the left thin film piezoelectric element 202 and a pair of electrode pads 206 are formed on the right thin film piezoelectric element 201. The right thin film piezoelectric element 201 and the left thin film piezoelectric (PZT) element 202 are coated and covered by a polymer 209, the polymer 209 includes a connection portion 911 at the place between the right and the left thin film piezoelectric (PZT) element 201, 202 to connect them physically. The right and the left thin film piezoelectric (PZT) element 201, 202 are laminated structures, and respectively include a first piezoelectric thin film layer 22 and a second piezoelectric thin film layer 25, and the two thin film layers 22, 25 are laminated together by adhesive 28. Specifically, the first piezoelectric thin film layer 22 includes a first electrode layer 223, a second electrode layer 224 and a first piezoelectric layer 222 sandwiched between the first electrode layer 223 and the second electrode layer 224, the second thin film layers 25 includes a third electrode layer 256, a fourth electrode layer 257 and a second piezoelectric layer 225 sandwiched between the third electrode layer 256 and the fourth electrode layer 257, the adhesive 28 is coated between the second electrode layer 224 and the third electrode layer 256 to bond the first and the second piezoelectric thin film layer 22, 25 together.
FIGS. 3a-3d show a conventional method of manufacturing the thin film piezoelectric element. Firstly, as shown in FIG. 3a, laminating a first electrode layer 223, a first piezoelectric layer 222 and a second electrode layer 224 on a substrate 11 in succession to form a first piezoelectric thin film layer 22, and laminating a fourth electrode layer 257, a second piezoelectric layer 225 and a third electrode layer 256 on a substrate 12 in succession to form a second piezoelectric thin film layer 25. Further referring to FIG. 3b, bonding the two piezoelectric thin film layers 22, 25 with the substrate 11, 12 respectively thereon together by an adhesive 28. Then, as shown in FIG. 3c, removing the substrate 11 by chemical etching or other similar technique. Finally, as shown in FIG. 3d, removing the second substrate 12 to form the thin film piezoelectric element.
However, due to the process limitation, especially the chemical etching accuracy control limitation, the process yield for the above-mentioned thin film piezoelectric element is very low. Moreover, since there are two piezoelectric thin film layer are bonded together by an adhesive, the process is very complex and expensive, and it is easy to cause the piezoelectric thin film peeling. In addition, there are two substrate-removing processes in the process, which may cause a high reject rate and in turn, increase the manufacture cost.
Hence, in order to lower cost and eliminate the adhesive process to increase the process yield, a design of a piezoelectric element having only a single piezoelectric thin film layer is put forward, however, the stiffness and flexibility of a single piezoelectric thin film layer is too weak to operate and it is easy to be damaged during its manufacturing and assembly process, thus it still can not increase the production efficiency and the rate of finished products.
Thus, it is desired to provide an improved thin film piezoelectric element and its manufacturing method to overcome the above-mentioned drawbacks.